a) Field of the Invention
The invention is a novel stack application related to improved carbon dioxide and particle removal and collection from flue gases produced during coal power-generation processes. More particularly, the invention is related to the direct sequestration of carbon dioxide in pulverized coal fired plants.
b) Description of Related Art
Combustion of carbonaceous materials accounts for the majority of the heat energy generated from fossil fuels. Heat energy is used to generate electrical power and/or for heating applications. Energy produced from combustion of carbonaceous materials constitutes more than 50% of the power and heat production. The final products of the combustion of fossil fuels for power generation are gaseous products, such as carbon oxides, and ash particles. Sulfur and nitrogen compounds in coal may form oxides during the combustion process. Means have been developed by those who are skilled in the art to address the formation, control and post combustion removal of the oxides of sulfur and nitrogen. These gaseous oxides tend to form acids of sulfur and nitrogen, and therefore they are called xe2x80x9cacid gasesxe2x80x9d. Acid gas emission control processes are reported in various technical references and textbooks, and therefore further explanation of such is not necessary.
Traditionally, after the post combustion treatments of the oxides of sulfur, nitrogen, and other particles, the flue gas still contains a minute amount of particles, which may not be feasible for removal by conventional particle or dust removal processes, such as electrostatic precipitation and fabric filtration. Electrostatic precipitation is unable to capture small particles in the near micro or sub-micron size range. This is indicated in most commercially available electrostatic precipitator particle collection units by efficiency curve data. As the particle size approaches a sub-micron size, the collection efficiency drops drastically. Additional improvement of particle capture efficiency can be expected by increasing the residence time for the flue gas inside the electrostatic precipitator train, which can be achieved by adding more electrostatic precipitation units. However, economical, technical, and space or xe2x80x9cfoot printxe2x80x9d considerations may rule out the option of additional residence time being provided by this method. This problem is acute for most of the existing coal-fired power plants.
Electrostatic precipitation (ESP) is an age-proven technology for the capture of fine particles from coal combustion. An electrostatic force is generated by the electrically charged particles and an electrically charged electrode causes the particles to migrate to collecting surfaces possessing an opposing electrical charge. One design consideration is the time for the charged particles to migrate to the collecting surface, which should be shorter than the particle residence time in the ESP confinement. Economic constraints may dictate the optimum design for the ESP dust collector. Variations in the electrical resistivity of the dust particles may also affect the ability of the particles to retain an electric charge. Resistivity of the particles may drastically reduce the intended dust collection efficiency. Industrial field data of electrostatic precipitator performance often show a drop in the collection efficiency for the sub-micron particles. This is mostly due to Brownian or Maxellian motions of small particles.
Alternatively, the use of fabric filtration utilizes the impaction, interception, and random motion of the particles on a fabric target for capture. Because of the low inertia of the small particles, the particles remain within the confinement of the stream lines, or become entrained in the stream lines of the filtering flue gas stream. Therefore, the particles are less likely to wander out of the confinement of these stream lines, and be captured by impaction and/or interception. The chances of random movement of the small particles being captured are even less. As a consequence, even with fabric filters, the likelihood of achieving sub-micron particle capture is not promising. Granted, the retention efficiency can be increased at the expense of deep filtration with a high pressure drop.
Sub-micron particles are a major recent concern for the public. The deposition of respirable particles inside human lungs can lead to the cause of emphysema and many respiratory diseases. The recent promulgation by the U.S. Environmental Protection Agency (EPA) on sub-micron size particle control regulations will add to the aforementioned considerations for design and operation of carbonaceous fuel power generation plants. Small particles and aerosols may elude the capture of thin felt or fabric filters, which have a lower number of fibers for, capture. The use of filtration technology for small particle removal is very similar to that of an ANDERSON IMPACTOR(copyright) air sampler for small particle retention. These mechanisms for small particle retention, such as impaction, interception and random motion, are still useful in somewhat limited applications. Emission control of sub-micron size particles needs to be addressed, however.
From an engineering or accounting point of view, the build up of carbon dioxide in the atmosphere is a matter of inventory. Inventory of carbon dioxide is the net result of carbon dioxide input, or generation, minus the carbon dioxide output, or depletion. One must keep in mind that carbon dioxide is formed in a matter of seconds by means of combustion or other related processes. The consumption of carbon dioxide is carried out in terms of bio-chemical or physiological reactions, generally several orders slower than the combustion processes. From an economic point of view, installations other than Mother Nature will be immense in scale and consequently costly in investment.
Addressing the carbon dioxide issue can be cost prohibitive. There is no apparent economical incentive for the developing countries to abide by practices for carbon dioxide sequestration. Many businesses in developed countries are reluctant to reduce their carbon dioxide emissions while developing countries continue to generate carbon dioxide. The production of economically attractive by-products may induce developing countries to adopt the practice of including carbon dioxide sequestration in their fossil fuel power plants. This appears to be logical, and conducive for carbon dioxide sequestration.
Another consideration for the installation of carbon dioxide sequestration facilities in conventional coal or carbonaceous power plants is the space or xe2x80x9cfoot printxe2x80x9d concern. Age-old coal firing power plant design practices leave very little space for an after-thought addition for pollution and carbon dioxide sequestration equipment.
The smoke stack is an ancient solution to the dispersion of flue gas and the products of combustion. The requirement to spread the products of combustion to a wide area or space calls for a tall structure. To facilitate the large volume disposal and dispersing of the gaseous products of combustion and its accompanying fine particles, an induction fan is required to move the gaseous products of combustion up through the stack or chimney. The thermo-siphon effect of the hot flue gas will also propel the gaseous products through the stack. In the past, the chimney or stack served a singular purpose of dispersing the gaseous products of combustion. There are numerous articles and software dealing with stack selection and design in the literature. Therefore, it will be redundant to retell the state of the art in stack design.
A main component of the United States power generation systems is the conventional pulverized coal-fired boiler, which produces high pressure and high temperature steam for electrical power generation in a traditional Rankine cycle. More than half of the U.S. domestic electric power is derived from conventional pulverized coal-fired power generation systems. Eighty-five percent of power generation for transportation and power generation is produced by the combustion of fossil fuels. The current concern for global warming is believed to be partially due to carbon dioxide emissions from fossil fuel combustion by internal combustion engines and from power generation. Measures to reduce carbon dioxide emission appear to be a logical avenue. Attempts to reduce the emission of carbon dioxide through energy conversion efficiency improvement were determined to be limited. As pointed out by a recent study by the Massachusetts Institute of Technology (MIT), the most cost effective avenue would be the direct sequestration of carbon dioxide.
The direct sequestration of carbon dioxide from mobile sources, i.e. motor vehicles, has been found to be inadequate and impractical. Given that the largest fraction of power generation comes from coal, the main avenue open would be the direct sequestration of carbon dioxide from coal-fired power generation plants. An emerging power generation activities in the world is direct coal combustion. There are few discernible means of coal power generation in the distant future other than conventional coal firing. Therefore, direct sequestration of carbon dioxide in the pulverized coal directly in coal-fired power plants is an attractive alternative solution.
Carbon dioxide, which has been excited by light, can be induced to react with water in the presence of chlorophyll. This is known as the photosynthesis reaction. There is no need to have an elaborate discussion of the photosynthesis reaction here, as there are many publications available on this subject. However, the primary product of carbon dioxide and water that undergo a light accelerated photosynthesis reaction in the presence of chlorophyll is glucose. Glucose is a stable carbohydrate, which can be used as animal feed, for alcohol fuel production, and as nutrients for plant growth.
Water, carbon dioxide and chlorophyll in algae are plentiful in the coal-fired power plant cooling water ponds. One question is how to obtain the light necessary to accelerate the photosynthesis chemical reaction. To look directly into the open flames inside a pulverized coal boiler combustion chamber with the naked eye is not feasible. A light shield (cobalt glass) usually is used to protect human eyes from the light of the flame. As the highly excited carbon dioxide gaseous molecules, formed from coal combustion, drop to a lower energy state, light is emitted. This light is in the infrared range and capable of the excitation of carbon dioxide gaseous molecules in the flue gas. Moreover, it is also known that a mixed light source, such as sunlight, can also prompt a photosynthesis reaction. It is not possible for the excited carbon dioxide molecules to react inside the highly oxidative combustion environment. Any products formed by the irradiation of carbon dioxide by infra-red light will be readily oxidized. In this environment, chlorophyll will simply be incinerated.
Conventional coal-fueled boilers have two essential elements, a combustion chamber to generate heat by fossil fuel combustion, and a heat recovery section to recover the heat of combustion by steam generation. The products of coal combustion are cooled and prepared for disposal. A stack or chimney is used to disperse the gaseous combustion products.
The advantages over the above described prior art and objects of the invention involving novel uses of a stack, follow.
It is an object of the invention to provide a means for a carbonaceous firing power plant to generate a by-product which is useable for producing fertilizer and/or animal feed stocks, to defray the cost of including carbon dioxide sequestration systems in existing power plants.
It is a further object of the invention to utilize existing equipment by means of a dual-functional application to reduce the cost of complying with the needs of adding pollution control and/or carbon dioxide sequestration systems.
It is another object of the invention to provide a system fully compatible with existing pulverized coal coal-fired power plants. Supporting facilities, such as cooling water ponds and related systems, can also serve as a surge tank for algae growth.
A specific object of the invention is to produce glucose as a by-product, which can be used as a nutrient for plant and animal growth. Algae are food for fish that thrive on glucose-containing water.
It is a further object of the invention to achieve a reduction in fine dust by virtue of a long residence time in a centrifugal force field and cascading aqueous streams to prevent re-entrainment of captured dust particles.
An advantage of the invention is to offer no added xe2x80x9cfoot-printxe2x80x9d concerns. The stack is an existing structure with plenty of space for the dual functions of dust capture and carbon dioxide sequestration.
A further advantage provided by the invention is that it is not capital intensive and it can also generate useful by-products for developing countries in Asia, South America, Africa and the former Soviet Union countries in Eastern Europe. Such countries have an economic incentive to try this approach, because of the added by-products and potential cost benefits.
In accordance with the invention, light extracted from the coal combustion chamber is used to accelerate or excite the carbon dioxidexe2x80x94water reaction in the presence of algae, inside a stack or other facilities where carbon dioxide and water come into contact, to form a glucose-like material for carbon dioxide sequestration.
Collection efficiency is improved by a cascading water film on the inside of the stack, and on surfaces of an optional internally mounted vortex generator, eliminating the re-entrainment of small particles and facilitating transport of the captured particles in the form of low concentration slurry.
The stack can also be utilized as a photo-chemically activated or biological reactor to promote the photosynthesis reaction between carbon dioxide and algae-laden water to form a carbohydrate substrate for carbon dioxide sequestration and utilization. The most prevalent product of the photosynthesis reaction would be glucose and/or its likes. Glucose is most useful for fertilizer and animal feed materials.
The vortex generator can also be made of light transmitting materials such as fiber optical material, which can transmit and emit light to promote photochemical reactions.
The vortex generator may also be made in the form of perforated plates and baffles to increase the contact between carbon dioxide rich flue gas and water in the presence of chlorophyll materials.
The increase in the flue gas tangential inlet velocity in a stack subjects upward-flowing flue gas to a centrifugal force field, thereby propelling entrained solid particles in the flue gas to the stack wall for more efficient collection.